The present invention relates generally to a protector for secondary batteries, and particularly to a protector for a specific secondary battery of high energy density, e.g., a lithium ion battery using a lithium ion doping or de-doping material as an active negative electrode material. More particularly, the present invention is directed to a battery protector of small size.
A lithium ion battery using a lithium ion doping or de-doping carbonaceous material can output high voltage and has high energy density albeit being light in weight, and so is now widely used on portable equipment. Although secondary batteries may be used over and over by charging, yet their performance may become worse upon charging. Especially in the case of a lithium ion battery, an overcharge preventing protector is incorporated therein so as to prevent overcharging which may otherwise cause precipitation of metallic lithium or an electrolyte leakage due to the actuation of a pressure valve due to gas generation upon overcharging, resulting in thermal runaway, and fuming. In addition, an over-discharge protector, a current limiter, a device for preventing a battery temperature increase during charging and discharging are provided.
Equipment using batteries as a power source may operate with batteries having different capacities and a different number of batteries depending on what purpose it is used for. Used for this reason is a battery pack which is attachable to or detachable from equipment and contains one or more batteries.
A battery protector should be regulated for each battery capacity, and so is built in the battery pack. This is also true of a positive temperature coefficient element (PTC) that can be actuated by heat generated by an overcurrent due to short-circuiting or a battery temperature increase to cut off a current passing therethrough, because it should be located in the vicinity of a battery.
Small yet large-capacity batteries are required for size reductions of equipment using batteries as a power source. However, a battery protector is built in an individual battery pack. This, combined with the size limitation of the battery pack, is one factor of a reduction in the amount of active battery materials.
The present invention is directed to a protector for a secondary battery having high energy density such as a lithium ion battery using a lithium ion doping or de-doping carbonaceous material as an active negative electrode material. A particular object of the invention is to provide a battery protector of small size.